Though the ePub may get validated by the ePubcheck but sometimes some errors may creep up that might affect the overall quality of the eBook. Here is a checklist that can be helpful in case you face such problems:-

1. epubcheck-3.0b4: Verify that the ePub has passed “epubcheck-3.0b4″. If the ebook has any error, then the eBook will not be uploaded successfully.

2. Metadata: Check that the fields in the Metadata are filled as per the guidelines.

3. Cover Image: When the ePub is dragged and dropped to ITUNES, check that the ebook is showing its Cover Image.

If cover is not displayed then most common cause is missing “<meta name=”cover” content=”cover-image” />” in OPF file.

OR

ID of <item> is “cover-image”

<item id=”cover-image” href=” Cover.jpg” media-type=”image/jpeg” />

4. Frontmatter pages: Check all the text present on Frontmatter Pages like Title Page, Half-Title Page, Copyright Page etc. These pages should have zero defect count.

5.Image Color Profile: Check the ePub on the Adobe Digital Editions. If any image is not displayed with the correct tagging, then the problem might be because of Image Color Profile. Images should have RGB Profile.

6.NCX view: Use Adobe Digital Editions to check book NCX(Right Side Navigation). All sections should be linked to correct references.

7. Cross-references: Check randomly for cross references and URLs present within the ebook.

8. Two column layout: Check the ebook in two column layout, specifically for images. If Images are flowing across columns, then add below CSS property in Stylesheet.
img {max-width:100%;}

9. Background colors: Check whether the text and the background colors are retained in the output formats.

10. Resolution: Check that all the images have resolution below 20 Lac pixels as Apple does not accept images with resolution more than that.